This page shows a noise series for ISO 100/200/400/800/1600/3200 to show real world differences. As with the other examples, all noise reduction was disabled except for long exposure noise reduction.
I’ve long felt that lab tests for noise are not particularly informative as to the visual impact of noise, and how it affects both color and sharpness. A real-world image can be helpful in understanding the degree to which noise can be tolerated.
Note also that detailed images like this one tend to hide noise, making it less apparent. Images with continuous tones, saturated primary colors, etc can make noise look much worse than it will here. For example, see the Kitchen Counter example and examine the red tomatoes.
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